From the first galaxies to today's Milky Way with the largest multi-narrow-band (Ha+Lya) surveys

David SobralIA/CAAUL & Leiden Observatory

AbstractI will present the results from the deepest and widest narrow-band surveys ever undertaken with the best 4-8 m telescopes (CFHT, UKIRT, Subaru and the VLT); a unique combined effort to select large, robust samples of (mostly) H-alpha (Ha) star-forming galaxies at z=0.20, 0.40, 0.8, 0.84, 1.47 and 2.23 (corresponding to look-back times of 2, 4.2, 7.0, 9.2 and 10.6 Gyrs) in a uniform manner over ~2-10 deg2 in the COSMOS, UDS and SA22 fields. Our results reveal the exponential decline of the typical star-formation rate of galaxies (SFR*) over the last 11 billion years, and very little evolution in the stellar mass function of star-forming galaxies, with strong implications to the main drivers of galaxy evolution. Our Ha star formation history also implies a stellar mass density growth which is in perfect agreement with independent observations of the stellar mass density growth over the last 11 billion years, finally resolving the worrying disagreement seen in the literature. Our large and homogeneously selected samples of Ha emitters across cosmic time are also being used to conduct detailed resolved dynamics (e.g. SINFONI, KMOS), dust (e.g. Herschel, Spitzer, ALMA), clustering, environment, and (resolved) metallicity studies (e.g. KMOS, FMOS). Surprisingly, we find that apart from the exponential decline in SFR* from high to low redshift, the statistical properties of the overall star-forming population reveal a remarkable non-evolution in the last 11 billion years. We argue that, to first order, most of the previously claimed evolutionary trends (for SF galaxies) are a direct consequence of the typical SFRs of galaxies being much higher in the past. Finally, I will talk about our efforts to extend our studies to the first 2-3 Gyrs of cosmic time using very wide-field (>10 deg2) Lyman-alpha narrow-band surveys at 2<z<9 (with CFHT, Subaru and the INT), including a very large double blind Lyman-alpha - Ha survey at z=2.23. I will finish by showing a handful of promising candidates that we are following-up with the VLT and WHT and that may be confirmed as the most distant sources ever found.